CN101719738B - High-efficiency solar concentration photovoltaic system - Google Patents

Abstract

The present invention relates to photovoltaic power generation technology, in particular to a high-efficiency solar concentrating photovoltaic system, which is composed of an optical concentrating device, a photovoltaic cell, an external circuit, a cooling plate and an external tracking device packaged in a casing. The optical concentrating device It is composed of a condenser and a homogenizing rod inserted in the central hole of the condenser. The upper and lower surfaces of the condenser are high-order aspheric mirrors, and the lower end of the homogenizing rod is directly seated on the photovoltaic cell. The diameter is equal to the caliber of the photovoltaic cell, and its height is the intercept between the high-order aspheric surface fitted on the lower surface of the condenser and the optical axis. This system overcomes the defects of low concentration ratio, small receiving angle and low light energy transmission efficiency in the current solar concentrating photovoltaic system. The system has a large receiving angle, high concentration, high energy transfer efficiency, simple structure and compact structure. advantage.

Description

High-efficiency solar concentrated photovoltaic system

technical field

The invention relates to photovoltaic power generation technology, in particular to a concentrating photovoltaic system that utilizes solar energy efficiently.

Background technique

Solar energy, as the main renewable energy in the future, has been paid more and more attention by various countries, and related researches have shown its huge application potential. However, so far, the application of photovoltaic technology in the electronic market has not achieved the expected results. One of the main reasons is that the cost of photovoltaic systems is too high. The cost of the photovoltaic system is dominated by the cost of photovoltaic cell materials and system tracking. It can be seen that the key to realizing large-scale industrialization of photovoltaic technology lies in reducing the cost of battery materials and system tracking.

An effective way to reduce the cost of battery materials and tracking costs is to add a low-cost optical condenser to the photovoltaic system to form a concentrated photovoltaic system. However, most of the concentrating mirrors in traditional concentrating photovoltaic systems are designed based on imaging focusing theory, such as trough parabolic reflectors, Fresnel line focusing, point focusing transmission mirrors, etc. Its common disadvantages are that the light concentration ratio is not high, the acceptance angle is small, the light energy transmission efficiency is low, and the aspect ratio is large.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned defects existing in the current solar concentrating photovoltaic system, and propose a high-efficiency solar concentrating photovoltaic system based on non-imaging theory, which has a large acceptance angle, high concentration, high energy transfer efficiency, The advantages of simple and compact structure.

The high-efficiency solar concentrating photovoltaic system of the present invention is mainly composed of an optical concentrating device packaged in a casing, a photovoltaic cell, an external circuit, a heat dissipation plate and an external tracking device. The uniform light rod in the core hole is composed of a uniform light rod, the lower end of which is directly seated on the photovoltaic cell, its diameter is equal to the aperture of the photovoltaic cell, and its height is the high-order aspheric surface fitted on the lower surface of the condenser lens and The intercept of the optical axis; the upper and lower surfaces of the condenser are high-order aspheric mirrors that meet the following formula:

$\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cr"\; filenames="H2009102180629E00011.png,H2009102180629E00013.png"\; state="\{\{state\}\}">cr</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; c</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="r"\; filenames="H2009102180629E00011.png,H2009102180629E00013.png"\; state="\{\{state\}\}">r</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; +</span>\underset{\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 20</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; i</span>}}$

In the formula, z is the sagittal height, c is the radius of curvature of the vertex, k is the cone coefficient, r is the distance from the point on the surface to the optical axis, and α _i is the coefficient of the polynomial.

The aperture D of the condenser is determined according to the etendue equal equation E _i =E _o , where E _i =2πDsinθ _i , E _o =2πnd sinθ _o , namely:

D＝nd sin(θ _o )/sin(θ _i )

Among them, d is the caliber of the photovoltaic cell, θ _i is the receiving half angle, θ _o is the irradiation angle of the receiving end of the homogenizing rod, and n is the refractive index of the material of the condenser; the lower surface of the condenser is coated with a reflective film.

In order to further improve the condensing effect, a reflective film is also coated on the central area of the upper surface of the condensing mirror, and the diameter of the coating area is 12%-13% of the caliber D of the condensing mirror.

The working principle of the present invention is: the sun beam is first incident on the upper surface of the condenser, and reaches the lower surface of the condenser after undergoing a refraction, and then returns to the upper surface of the condenser after experiencing a reflection, and reaches uniform light after a total reflection. At the incident end of the rod, the solar beam is uniformly lighted by the uniform rod, and finally irradiates the upper surface of the photovoltaic cell to realize high-efficiency photoelectric conversion, and the generated current is derived from the external circuit. In order to avoid photoelectric loss of the system due to overheating of the photovoltaic cells due to long-term exposure, we connect a heat sink to the back of the photovoltaic cells. Eventually the device was installed on a tracking device to track the sun in real time.

The key technology of the present invention lies in the design of the optical components. When designing, the condenser lens and the homogenizing rod are firstly designed separately, and then processed as a whole during processing, which is beneficial to the installation and adjustment of the system (avoiding the introduction of installation and adjustment errors), and reduces the complexity of the system. It is also more conducive to reducing the overall system cost.

The theoretical basis for the design of the high-magnification condenser lens of the present invention is the non-imaging theory. First, to maximize the energy of the incident beam to the receiving end, it must be ensured that the etendue E _i of the incident beam is equal to the etendue E _o of the outgoing beam, that is, E _i =E _o . Secondly, it must be ensured that the edge rays at the incident end of the system match those at the exit end, that is, the principle of edge rays. Under this premise, the light between the two edge rays will also irradiate into the two edge points of the receiving surface, in other words, the light rays with other incident angles smaller than the maximum acceptance angle can be irradiated between the two edge points of the receiving surface Between, here, the two edge points of the receiving surface refer to the left and right endpoints of the incident end of the dodging rod.

The high-efficiency solar concentrated photovoltaic system of the present invention has the following outstanding advantages:

1. A larger receiving angle can be obtained: 0.5 to 5 degrees, which means that the tracking accuracy of the solar photovoltaic system can be greatly reduced, and the tracking cost is correspondingly reduced.

2. Quite high geometric concentration ratio: 30,000-300, which relatively reduces the area of photovoltaic cells and saves photovoltaic cell materials, that is, greatly reduces the cost of the entire system.

3. The aspect ratio is generally less than 0.5, and the structure of the entire photovoltaic concentrating system is very compact, which is conducive to large-scale array integration.

4. The energy transmission efficiency is more than 80% (considering the refraction, reflection loss and absorption loss, etc.), the light energy loss is very small, and the solar energy is used more efficiently.

5. The precision of the surface shape is not high. Compared with the concentrator based on imaging theory, the surface precision of the concentrator of the present invention is not very high, which is more conducive to the use of organic material PMMA injection molding, large-scale processing and production of the concentrator, thereby greatly reducing the cost of photovoltaic systems.

Description of drawings

Fig. 1 is the structural representation of efficient solar concentrating photovoltaic system of the present invention;

Fig. 2 is a schematic diagram of the design principle of the high-magnification condenser lens of the present invention. The dotted line in the figure represents the homogenization rod;

Fig. 3 is a schematic diagram of light gathering under the positive maximum receiving half-angle situation after truncating according to the present invention;

Fig. 4 is a schematic diagram of light gathering in the case of a negative maximum receiving half-angle after being truncated in the present invention;

Fig. 5 is a diagram of the relationship between the energy transmission rate and the angle of the concentrator of the present invention when the acceptance angle is 2.7 degrees and the concentrating ratio is 500 times. (Do not consider dielectric absorption, refraction, reflection loss, and the center of the upper surface is coated with a reflective film).

Detailed ways

The present invention will be described in further detail below in conjunction with the embodiment given with accompanying drawing.

Referring to Fig. 1, a high-efficiency solar concentrating photovoltaic system is mainly composed of an optical concentrating device (1), a photovoltaic cell (3), an external circuit, a cooling plate (4) and an external tracking device packaged in a casing (5). Before starting the design, we first select the cell size, choose a smaller planar photovoltaic cell, circular, with a diameter of d=2mm, and a device acceptance angle θ _i =2.7°. Next, determine the geometric concentration ratio C. According to the geometric concentration ratio formula C=(n/sinθ _i ) ² , where n is the refractive index of the condenser lens, we select PMMA: n=1.5, and the geometric concentration ratio can be obtained: C= 1014. Then according to the etendue equal equation E _i = E _o (where E _i = 2πD ₀ sinθ _i , E _o = 2πnd sinθ _o , in order to achieve the maximum concentration, generally θ _o = π/2), we can obtain the aperture of the condenser D=ndsin(θ _o )/sin(θ _i )=ndsin(π/2)/sin(2.7)=63mm.

Concrete design steps of condenser lens of the present invention are as follows:

Step 1: Select any curve as the upper surface of the condenser, as shown in 1.1 in Figure 2(a). The curve should be as smooth as possible, generally choose a quadratic curve.

Step 2: Construct the negative incident marginal ray family-p, as shown in Figure 2(a) 6. According to the principle of marginal rays, this part of the light beam is refracted by the upper surface 1.1 of the condenser, reflected by the lower surface 1.2, and then fully reflected by the upper surface 1.1, and should reach the left end point of the exit end, that is, the left end point 2.1 of the uniform light rod, combined with the equal optical path and According to the laws of refraction and reflection, we can obtain the lower surface 1.2 of the condenser.

Step 3: Construct the positive incident marginal ray family +p, as shown in Fig. 2(b) 7. Also according to the principle of marginal rays, this part of the light beam is refracted by the upper surface 1.1 of the condenser, reflected by the lower surface 1.2, and then totally reflected by the new upper surface 1.3, and should reach the right end point of the exit end, that is, the right end point 2.2 of the uniform light rod. Again, according to the equal optical path and the law of refraction and reflection, we can obtain the new upper surface 1.3 of the condenser.

Step 4: If the new upper surface 1.3 is close enough to the upper surface 1.1 in step 2, our design process ends, otherwise, repeat steps 2 and 3 until the design requirements are met.

Step 5: Analyze the total reflection on the upper surface of the condenser. According to the analysis of the final design results of the condenser, it is known that a small part of the upper surface near the optical axis does not meet the total reflection condition, and the range of the reflective coating area needs to be calculated.

The above design process may not always converge, it depends on whether any curve taken in step 1 is suitable, once the design process does not converge, we can choose a smoother curve as the upper surface 1.1 of the condenser, and start the design process again until we meet design requirements.

From the above design process, we can generally obtain more than 1,000 data points on the upper and lower surfaces of the condenser, and then use the aspheric high-order polynomial based on the least squares method to fit the data points to obtain a 2D curve. The 3D surface is obtained by rotating the 2D curve around the axis of symmetry.

Finally, the upper surface 1.1 of the concentrator obtained by our fitting satisfies the following aspherical equation:

$\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cr"\; filenames="H2009102180629E00011.png,H2009102180629E00013.png"\; state="\{\{state\}\}">cr</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; c</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="r"\; filenames="H2009102180629E00011.png,H2009102180629E00013.png"\; state="\{\{state\}\}">r</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; +</span>\underset{\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 20</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; i</span>}}$

Fitted aspheric coefficients: c=0, k=0, other high-order polynomial coefficients are:

α ₁ =-2.968723752057118e-002 α ₂ =9.578901915412360e-003

α ₃ =-1.054537717243669e-003 α ₄ =-6.553014937945029e-003

α ₅ =-1.296080897617321e-004 α ₆ =8.154575515178800e-005

α ₇ =1.174455186859848e-004 α ₈ =3.596494741656907e-005

α ₉ =6.774150382578909e-007 α ₁₀ =9.049049829938531e-007

α ₁₁ =9.013708058464528e-008 α ₁₂ =6.844174049336993e-009

α ₁₃ =3.995979286701326e-010 α ₁₄ =1.793400727048338e-011

α ₁₅ =6.134389965925459e-014 α ₁₆ =1.570168537821995e-014

α ₁₇ =2.911123308884652e-016 α ₁₈ =3.691113208473048e-018

α ₁₉ =2.862557790283019e-020 α ₂₀ =1.023908352475696e-022

The lower surface 1.2 of the condenser lens also satisfies the following aspherical equation:

$\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cr"\; filenames="H2009102180629E00011.png,H2009102180629E00013.png"\; state="\{\{state\}\}">cr</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; c</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="r"\; filenames="H2009102180629E00011.png,H2009102180629E00013.png"\; state="\{\{state\}\}">r</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; +</span>\underset{\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 20</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; i</span>}}$

Fitted aspheric coefficients: c=0, k=0, other high-order polynomial coefficients are:

α ₁ =8.063349804964906e-003 α ₂ =2.643189651057634e-002

α ₃ =1.495787427468164e-003 α ₄ =-6.842429168186267e-003

α ₅ =-6.975081732538938e-004 α ₆ =-3.563992090534584e-003

α ₇ =-1.163479728523440e-003 α ₈ =-2.656457882329482e-004

α ₉ =-4.449383419358939e-005 α ₁₀ =-5.623839924370509e-006

α ₁₁ =-5.456138282119727e-007 α ₁₂ =-4.100576430850643e-008

α ₁₃ =-2.394016870217314e-010 α ₁₄ =-1.082133698314836e-010

α ₁₅ =-3.748361315024322e-012 α ₁₆ =-9.758465287902727e-013

α ₁₇ =-1.846908194829235e-014 α ₁₈ =-2.398002986017931e-017

α ₁₉ =-1.909588979925858e-019 α ₂₀ =-7.030515308414840e-022

The diameter of the homogenizing rod 2 is the battery size d=2mm, and the length is equal to the y-axis intercept 14.2mm of the polynomial curve fitted to the lower surface of the condenser by 1.2.

The lower surface of the condenser 1.2 needs to open an axial hole whose size matches the size of the homogenizing rod near the axis. The opening diameter d _ht of the top end is: d _ht = 2mm, and the opening diameter d _hb of the bottom end is: d _hb = 5mm. The depth is 14.2mm from the height of the dodging rod.

The lower surface 1.2 of the condenser is coated with a reflective film on the full aperture, and the upper surface is coated with a reflective film near the central axis, and its diameter D _m is: D _m =D*13%=63*0.13=8.2mm.

In order to make all the light meet the total reflection condition in the homogenizing rod and further increase the light energy reaching the photovoltaic cell, we can optimize the structure of the condenser, that is, shorten the diameter of the condenser. Determined according to the etendue equal equation E _i =E _o , wherein E _i =2πDsinθ _i , E _o =2πndsinθ _o , the aperture of the truncated condenser lens can be obtained, but at this time the illumination angle θ _o =90-arcsin(1/ n). The truncated condenser aperture is:

D＝ndsin(90-arcsin(1/n))/sin( _θi )＝31.65mm

As shown in accompanying drawings 3 and 4, we use optical software to perform ray tracing on the truncated condenser lens system, and the results show that the solar beams 6 and 7 at the maximum acceptance angle just reach the endpoints 2.1 and 2.2 of the homogenization rod, and then After undergoing multiple times of total reflection by the homogenizing rod 2 , the solar beam is uniformly irradiated on the surface of the photovoltaic cell 3 to complete photoelectric conversion.

We can know by accompanying drawing 5, concentrating mirror of the present invention is a kind of efficient solar concentrating device, and the solar light beam in the acceptance angle can almost all gather to the photovoltaic cell surface, and can obtain the good uniformity on the surface of photovoltaic cell Light energy distribution.

Claims (2)

1. high-efficiency solar concentration photovoltaic system, mainly by the optical concentration device (1) that is encapsulated in the shell (5), photovoltaic cell (3), external circuits, heating panel (4) and external trace device form, it is characterized in that: described optical concentration device is by condenser (1) and be plugged on interior optical tunnel (2) formation of condenser (1) axle center hole, the lower end of described optical tunnel (2) directly is seated on the described photovoltaic cell (3), its diameter equates that with the bore of photovoltaic cell (3) it highly is the high order aspheric surface of condenser lower surface match and the intercept of optical axis; The upper and lower surface of described condenser (1) is the high order aspheric surface mirror that meets following formula:

$z=\frac{{\mathrm{cr}}^2}{1+\sqrt{1-(1+k)c^2{r}^2}}+\underset{1}{\overset{20}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_i{r}^i$

In the formula, z is that rise, c are that vertex curvature radius, k are that circular cone coefficient, r are that point arrives optical axis distance, α on the face type _iBe polynomial every coefficient,

The bore D of condenser (1) equates equation E according to optical extend _i=E _oDetermine, wherein E _i=2 π Dsin θ _i, E _o=2 π ndsin θ _o, d is photovoltaic cell bore, θ _iFor receiving half-angle, θ _oFor optical tunnel receiving terminal illumination angle, get θ _o=pi/2, n are the condenser Refractive Index of Material; Be coated with reflectance coating on the lower surface.

2. high-efficiency solar concentration photovoltaic system according to claim 1 is characterized in that, the central area of the upper surface of described condenser (1) is coated with reflectance coating, and the diameter of this coating film area is the 12%-13% of condenser bore D.

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